Jan Ruff

Skin sodium measured with 23Na MRI at 7.0 T

Skin sodium (Na+) storage, as a physiologically important regulatory mechanism for blood pressure, volume regulation and, indeed, survival, has recently been rediscovered. This has prompted the development of MRI methods to assess Na+ storage in humans (23Na MRI) at 3.0 T. This work examines the feasibility of high in‐plane spatial resolution 23Na MRI in skin at 7.0 T. A two‐channel transceiver radiofrequency (RF) coil array tailored for skin MRI at 7.0 T (f = 78.5 MHz) is proposed. Specific absorption rate (SAR) simulations and a thorough assessment of RF power deposition were performed to meet the safety requirements. Human skin was examined in an in vivo feasibility study using two‐dimensional gradient echo imaging. Normal male adult volunteers (n = 17; mean ± standard deviation, 46 ± 18 years; range, 20–79 years) were investigated. Transverse slices of the calf were imaged with 23Na MRI using a high in‐plane resolution of 0.9 × 0.9 mm2. Skin Na+ content was determined using external agarose standards covering a physiological range of Na+ concentrations. To assess the intra‐subject reproducibility, each volunteer was examined three to five times with each session including a 5‐min walk and repositioning/preparation of the subject. The age dependence of skin Na+ content was investigated. The 23Na RF coil provides improved sensitivity within a range of 1 cm from its surface versus a volume RF coil which facilitates high in‐plane spatial resolution imaging of human skin. Intra‐subject variability of human skin Na+ content in the volunteer population was <10.3%. An age‐dependent increase in skin Na+ content was observed (r = 0.78). The assignment of Na+ stores with 23Na MRI techniques could be improved at 7.0 T compared with current 3.0 T technology. The benefits of such improvements may have the potential to aid basic research and clinical applications designed to unlock questions regarding the Na+ balance and Na+ storage function of skin. Copyright

Sodium imaging of the heart at 7T: design, evaluation and application of a four-channel transmit/receive surface coil array

Background Insight of physiological processes and cellular metabolism makes 23Na-MRI conceptually appealing as non-invasive imaging discipline. Several studies report the applicability of 23Na-MRI for the detection and assessment of acute and chronic heart disease due to increased sodium concentration after myocardial infarctions. Bi-exponential decay of the signal and a low SNR compared to 1H-MRI makes 23Na-MRI unattractive for clinical use. With a high SNR and fast imaging technologies ultrahigh field MRI brings 23Na-MRI back into focus, asking for dedicated radiofrequency (RF) technology.

Accelerated fast spin-echo magnetic resonance imaging of the heart using a self-calibrated split-echo approach.

Purpose Design, validation and application of an accelerated fast spin-echo (FSE) variant that uses a split-echo approach for self-calibrated parallel imaging. Methods For self-calibrated, split-echo FSE (SCSE-FSE), extra displacement gradients were incorporated into FSE to decompose odd and even echo groups which were independently phase encoded to derive coil sensitivity maps, and to generate undersampled data (reduction factor up to R = 3). Reference and undersampled data were acquired simultaneously. SENSE reconstruction was employed. Results The feasibility of SCSE-FSE was demonstrated in phantom studies. Point spread function performance of SCSE-FSE was found to be competitive with traditional FSE variants. The immunity of SCSE-FSE for motion induced mis-registration between reference and undersampled data was shown using a dynamic left ventricular model and cardiac imaging. The applicability of black blood prepared SCSE-FSE for cardiac imaging was demonstrated in healthy volunteers including accelerated multi-slice per breath-hold imaging and accelerated high spatial resolution imaging. Conclusion SCSE-FSE obviates the need of external reference scans for SENSE reconstructed parallel imaging with FSE. SCSE-FSE reduces the risk for mis-registration between reference scans and accelerated acquisitions. SCSE-FSE is feasible for imaging of the heart and of large cardiac vessels but also meets the needs of brain, abdominal and liver imaging.